Generally, washing machines are electronic home appliances which remove pollutant and dirty of clothes and bedclothes using emulsification of a cleaning material and friction and impact of a water current by rotation of wash blades. An ordinary washing process in the washing machine includes a wash/rinse/dehydration stroke and a water supply/discharge stroke.
Washing machines are classified into a pulsator washing machine and a drum washing machine according to a wash mode. In the case of the pulsator washing machine, an inner tub is separated from a pulsator which is installed in the lower portion of the inner tub. In the case of wash and rinse strokes, only the pulsator rotates at a state where the inner tub has stopped, to thus cause a rotating water current, and in the case of a dehydration stroke, the pulsator and the inner tub rotate together.
In the case of an initial full automatic washing machine, an inner tub having a number of dehydration holes is rotatably installed in the inside of an outer tub which is installed in a case forming an external contour, a pulsator is rotatably installed in the lower-center of the inner tub, and a driving device having a clutch and a motor for making the inner tub and the pulsator is installed in the lower portion of the outer tub.
In such a full automatic washing machine, the motor is installed in one side of the lower portion of the outer tub, the clutch for controlling a rotational force of the motor is installed in one side of the motor, pulleys are combined with the lower ends of the axes of the motor and the clutch, respectively, and a belt is linked between the pulleys. Accordingly, the rotational force of the motor is transferred to the clutch via the belt, and the clutch controls the rotational force of the motor according to the respective strokes of the washing machine. As a result, the pulsator and/or the inner tub are made to rotate.
Thus, the driving device of the washing machine having the above-described structure has problems that driving the power decelerates when the rotational force of the motor is transferred to the dehydration axis and the wash axis which make the inner tub and the pulsator, and that concentricity of the inner tub occurs since the motor is attached on the side of the clutch.
In order to solve the problem that the concentricity of the inner tub occurs, an inner rotor style motor is attached not on the side of the clutch but on the lower end of the clutch. Accordingly, the problem that the inner tub is concentric has been solved. However, since a washing machine which is longer by length of the inner rotor style motor than that of a conventional washing machine, a problem that the washing machine becomes huge still remains.
Therefore, as disclosed in the Korean Laid-open Publication No. 2004-71420, an outer rotor style brushless direct-current motor (hereinafter, referred to as “BLDC motor”) is connected directly to the lower side of a clutch, to accordingly provide a driving device of a washing machine which prevents concentricity of an inner tub and size of the washing machine from being enlarged, and increases output of a drive motor of the washing machine.
However, the driving device of the washing machine which is disclosed in the Korean Laid-open Publication No. 2004-71420 is hard to satisfy a high power which is required in a high-capacity full automatic washing machine since the driving device has a single-rotor/single-stator structure as the outer rotor style BLDC motor. In addition, malfunction or breakdown of the motor may occur due to leakage of water in the washing machine.
In addition, a clutch assembly that controls rotation of a dehydration axis that rotates the inner tub at the dehydration stroke of the washing machine, emancipates a sliding coupler to thus intercept the rotational force from being applied to the dehydration axis, and makes the wash axis and dehydration axis integrally rotate at the wash/rinse strokes. As a result, components of the clutch assembly becomes complicated, and a brake assembly that disrupts rotation of the dehydration axis should be separately provided.
Further, an outer rotor style BLDC motor applied to a washing machine is disclosed in the U.S. Pat. No. 5,226,855. Here, in a drive system of the washing machine disclosed in the U.S. patent, a spin tub which is an inner tub is placed within a container which is an outer tub, and the spin tub and an agitator rotate by buoyancy of the wash water in the container at a state where the agitator is located at the center of the spin tub. That is, teeth of toothed wheels are freed by buoyancy of the wash water in the container, and thus the spin tub and the agitator freely rotate to thereby make the washing machine perform a wash stroke. In this case, if no wash water exists in the washing machine, the teeth of the toothed wheels are engaged with each other, to thus make the spin tub and the agitator simultaneously rotate and make the washing machine perform a dehydration stroke.
In the drive system of the washing machine disclosed in the U.S. patent, a coupling structure of the inner and outer rotating axes and the toothed wheels is complex since the agitator and the spin tub are made to rotate according to whether or not the wash water exists in the container. Further, since no gear unit that amplifies the rotational force that is generated from an outer rotor style BLDC motor is provided in the U.S. patent, the rotational force that is transferred to the agitator and the spin tub is not been properly controlled.
Therefore, a washing machine which may simplify a coupling structure between a wash axis which rotates a pulsator and a dehydration axis which rotates a spin tub and which may control the pulsator and the spin tub to selectively rotate, should be proposed.
Further, the inner rotor style motor has shortcoming that a gear ratio of a gear unit which transfers the rotational force of the motor should be high since the instantaneous torque of the inner rotor style motor is low. Meanwhile, the outer rotor style motor can reduce a gear ratio of the gear unit relatively, since the outer rotor style motor has a torque higher than the inner rotor style motor.
Thus, if an outer rotor style motor is applied to a washing machine, the ratio gear of the gear unit can be reduced in comparison with the case that an inner rotor style motor is applied thereto. However, the washing machine employing the outer rotor style motor does not satisfy high power of a large-capacity washing machine. Accordingly, a driving device of a washing machine which can satisfy high power of the large-capacity washing machine, and further reduce the ratio gear of the gear unit is required.
According to a BLDC motor of a double-rotor structure, permanent magnets are arranged at the inner and outer sides of a division type core, and accordingly a flow of magnetic flux in a magnetic circuit is formed by a yoke of the inner and outer side permanent magnets and a rotor. Thus, it is possible to perfectly divide the division type core. As a result, the double-rotor structure BLDC motor has a structure of greatly heightening productivity of the division type core and power of the motor by individual coil windings.
As described above, when a division type core is employed in a stator, a general-purpose winding machine can be used for coil-winding individual cores. Accordingly, an initial investment expense for preparing for such a general-purpose winding machine is very inexpensive in comparison with the case of an integral type core structure that uses an expensive dedicated winding machine. However, a new stator assembly structure which can effectively assemble a stator when a number of individual cores are assembled into an integral type to thus mutually connect coils, is required.
That is, a structure of arranging and fixing many division type core assemblies on a printed circuit board (PCB) to then connect coils, and a specific coupling structure of a double-rotor are required. Accordingly, in order to improve an assembly of a division type stator core through the Korean Patent Laid-open Publication No. 2005-245, a stator structure and a BLDC motor using the stator structure was proposed by the same applicant as that of the present invention, in which a number of stator core assemblies are automatically positioned in and fixed to an annular core support, so as to be connected with divided coil.
By the way, the core holder essentially requires for an insert molding process of integrally forming a pair of guide flanges and/or a number of coupling protrusion pairs which are necessary for automatically positioning a division type core assembly in a PCB for connection of an annular band structure having a number of conduction lines and bonding pads which are necessary for mutually connecting coil on the lower surface of the core holder.
Moreover, the core holder has a structure that a number of the division type core assemblies are temporarily assembled in an annular plate formed of the PCB and the pair of the guide flanges, to thereby attain a bulk molding compound (BMC) molding. However, since the BMC molding material has a feature that mutual coherence for the PCB annular plate is weak, a stator holder enclosing the upper and lower surfaces of the PCB has a small contact area between the upper/lower portions of the PCB. Accordingly, there is a problem that coherence is weak.
Therefore, when a stator of a BLDC motor of a double structure is insert-molded, a contact area of a BMC molding material should be maximized to thus maximize durability of a stator.